Gecko, Mussel Powers Combined in New Sticky Adhesive
John Roach
for National Geographic News
July 18, 2007

Give your tape some real "mussel"!

So might go the ad campaign for "geckel"—a next-generation adhesive inspired by the legendary stickiness of geckos and mollusks—if the product is successfully brought to market.

One of nature's greatest clingers, geckos have long fascinated scientists with the tiny hairs on their feet, which allow the tropical lizards to scurry up walls and across ceilings.

But tapes made by a number of research teams in recent years lose most of their adhesive strength underwater.

Phillip Messersmith, a biomedical engineer at Northwestern University in Evanston, Illinois, was intrigued by the problem.

He has been making liquid glues for several years based on the adhesive proteins of mussels that allow the mollusks to hold on tight to rocks and docks in even the roughest of waters.

"I thought, Well, what if we try to combine the mussel adhesive proteins ... with a gecko type strategy, which has its own set of properties?" Messersmith said.

"We might have something new and interesting and useful."

The result was geckel, a promising new adhesive described by Messersmith and colleagues in this week's issue of the journal Nature.

Geckel could one day replace stitches to close wounds or allow robots to roll up walls or along the seafloor, Messersmith noted.

Proof of Principal

The "proof of principal" adhesive, as Messersmith describes the few square-millimeter patch of tape, is reusable like a sticky note and works while wet or dry.

To make the tape, the researchers used an electron beam to pattern a mold for an array of tiny silicon pillars, each 400 nanometers wide and 600 nanometers tall. (A human hair is about 100,000 nanometers—or billionths of a meter—thick.)

Once the pillars were cast and peeled from the gecko-inspired mold, the team dipped them into a solution with the mussel-adhesive-inspired protein.

The tiny patch of geckel held together for more than a thousand contact-and-release cycles in both wet and dry environments, Messersmith said.

But for the technology to reach a mass market, researchers will need a faster and less expensive method, he added.

Few Years Away?

Ronald Fearing is the director of the Biomimetic Millisystem Lab at the University of California at Berkeley. His research team has developed a flexible array of gecko-like hairs.

He said that several of the gecko-adhesive teams have tested .15-square-inch (one-square-centimeter) pieces of tape and found they fall apart or get dirty after just a few contact-and-release cycles.

Similar wear-and-tear problems might also be encountered with a larger piece of geckel, he pointed out.

"It comes down to if you have a single stalk, it's hard for it not to stick," he said. "Getting millions of stalks all working together—so far, that's been a challenge for many groups."

However, Fearing and Messersmith both predict gecko- and mussel-inspired adhesives are just a few years shy of the market for applications like waterproof bandages or clingy clothing.